* tests/openpgp/all-tests.scm: Run each test twice, once with public
keys stored in a keybox, once with a keyring.
* tests/openpgp/defs.scm (create-gpghome): Create a public keyring to
make GnuPG use that instead of creating a keybox if '--use-keyring' is
given.
* tests/openpgp/setup.scm: Fix flag handling and usage.
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